An easy way to keep everything uniform is to base a lot of the terrain features on an old CD. They are flat, durable, and they accept paint and glue fairly well. One of my buddies made several swamp and forest pieces in this manner. Two-part modelling clay, some sticks from the yard, and a little flock should make some nice stands of bare trees. Make pools out of the same clay and paint the interior with a mix of green or brown paint and white glue. The glue is "poor-man's" water effect and gives a shiny finish to the paint.
Another buddy made uniform wall pieces by cutting out small blocks of insulation foam, drawing bricks on them with a pencil, and gluing them to large wooden tongue depressors. We painted them with the citadel spray gun and drybushed on a highlight. You can also download and print off brick-patterned designs from www.jennifersprintables.com. Just make sure you scale them down a bit. Print, glue to cardboard, base on a piece of heavy card. Done.
For buildings, the hirst arts molds are easy to use and give a professional result. I primarily use foamcore and cardboard. Tutorials are on my blog under "slum" and "frontier" tags. Since buildings take more time, focus on getting one or two done first and fill in the rest with other kinds of features.
We are also getting into Christmas season, so don't forget to look around the Christmas town displays for bridges, trees, and fences. Lemax, etc... make lots of cool stuff.
Pet store bargain bins will also be a good place to look. Some of my favorite pieces (ruins, skulls) are actually 99 cent cast-offs from the aquarium section.
Have fun!